1. Field of the Invention
The present invention relates to a power switching control apparatus and in particular to a power switching control apparatus which prevents a phenomenon which gives serious effects to a power system and devices connected thereto by controlling the switching timing of a switching device in a power system.
2. Description of the Related Art
Approaches to prevent a transient phenomenon which is severe to systems and power devices by controlling the switching timing of a circuit breaker in a power system have heretofore been proposed.
A Conference Paper No. 13-12 of International Conference on Large High Voltage Electric Systems held in August-September 1988 entitled "Synchronous Energizing of Shunt Reactors and Shunt Capacitors"0 discloses that transient inrush currents which are generated upon energization of shunt reactors or shunt capacitors can be remarkably reduced by closing a circuit breaker for shunt reactors at a peak of a voltage of a power source and by closing the circuit breaker for shunt capacitors at a zero value of the power source voltage. Since the magnetic flux induced in a core of a reactor is proportional to the integral of a voltage, the magnetic flux after 0.5 cycle from the time when the reactor is energized at the peak value of the power source voltage is just zero so that the flux is not saturated. Therefore, inrush currents generated due to saturation of magnetic flux through the core do not occur in this case. Even if the closing of the circuit breaker is slightly shifted from the peak point of the voltage, the saturation of the magnetic flux will be slight and the inrush currents can be suppressed to a low value within a narrow range. In energization of the capacitors, the capacitors are energized at a zero voltage so that no high frequency inrush current will be generated. Even if the capacitors are energized at a time slightly different from the point of zero voltage, the voltage applied to the capacitors is low and the high frequency inrush currents can be suppressed to a low value within a narrow range. However, application of this approach to a practical system has technical problems as follows:
(1) A transient phenomenon occurs on breaking, as well as on closing. Generation of reignition or restrike will induce an abnormal voltage. A synchronous energizing technique alone can not eliminate a possibility of damage in insulation of apparatus. PA1 (2) Circuit breakers are connected with various load devices. This synchronous energizing approach can be advantageously applied to a certain device while it may adversely affect on application to another device resulting in energization under worst conditions. It is very troublesome to mount different synchronous energizing devices to different load devices.